Chapter 11: Kin Selection and Social BehaviorOverview |
Social interactions create the possibility for conflict and cooperation. Consider two American crows (Corvus brachyrhynchos) patrolling the edge of their adjacent nesting territories. If one moves across the established boundary, its action may trigger aggressive calls, a flight chase, or even physical combat. But if a hawk flies by, the two antagonists will cooperate in chasing the predator away. Later in the day, these same individuals may spend considerable time and effort feeding the young birds in the nests in their respective territories, even though the nestlings are the crows’ siblings or half-siblings and not their own offspring.
When and why do these individuals cooperate with each other, and why do they help their parents raise their siblings instead of leaving home to rear their own offspring? What conditions lead to conflicts with each other and with their parents, and how are these conflicts resolved? In chapter 11 of your textbook you will explore the answers to these questions.
11.1 Kin Selection and the Evolution of Altruism Explaining altruistic behavior is a challenge for the Theory of Evolution by Natural Selection. Altruism is a central paradox of Darwinism. It would seem impossible for natural selection to favor an allele that results in behavior benefiting other individuals at the expense of the individual bearing the allele. For Darwin (1859: 236), the apparent existence of altruism presented a “special difficulty, which at first appeared to me insuperable, and actually fatal to my whole theory.” Fortunately he was able to hint at a resolution to the paradox: Selection could favor traits that result in decreased personal fitness if they increase the survival and reproductive success of close relatives.
In section 11.1 of your textbook you will learn more about altruism and its role in evolution.
11.2 Evolution of Eusociality Darwin (1859) recognized that social insects represent the epitome of altruism, and thus a special challenge to the theory of evolution by natural selection. Many worker ants and bees, for example, do not reproduce at all. They are helpers at the nests of their parents, for life. This is an extreme form of reproductive altruism.
Refer to section 11.2 of your textbook to about examples of eusociality in the animal kingdom.
11.3 Parent–Offspring Conflict The theory of kin selection has been remarkably successful in explaining the structure and dynamics of social groups such as bee-eater clans and wasp colonies. Now, we consider how the theory might inform questions about a more fundamental social unit: parents and offspring.
Refer to section 11.3 of your textbook to learn more about the parent-offspring conflict.
11.4 Reciprocal Altruism Inclusive fitness theory has been remarkably successful in explaining a wide range of phenomena in social evolution. In many cases, altruistic acts can be understood in light of Hamilton’s rule, and conflicts can be understood by analyzing asymmetries in coefficients of relatedness and differences in fitness payoffs. But the theory and data we have reviewed thus far are only relevant to interactions among kin. What about the frequent occurrence of cooperation among un-related individuals?
To learn the answers to these questions, turn to section 11.4 of your textbook.